I have read what I’m not sure is the "first chapter" or simply completed the one shot story. I was under the impression that it was, in fact, a "one shot" as it clearly states "Look forward to Hatori-sensei's new one-shot in LaLa issue 5!!" at the end of the “chapter” giving me the impression that what I also just read was a one shot. I would change it myself, but just making sure I'm right...?

Here you can see the answer:
http://omaris-sister.blogspot.com/2012/02/one-shot-datarame-mo usouryoku-opera-by.html#more

Thank you ^_^!